Oiasso, Oiasona or Oiarso was a Basque Roman town located on the left bank of the Bidasoa estuary in the Bay of Biscay (current Basque Country, in Spanish territory). Archaeological evidence unearthed recently pinpoints the core area of Oiasso in the old quarter of Irun (Gipuzkoa) by the Spanish-French border, where harbour and bath remains have been discovered. However, two other focuses in Cape Higuer and hermitage Ama Xantalen (necropolis and mausoleum) point to a wider complex outside the main nucleus.